Fluid energy mills or jet mills are well known and widely used for the pulverizing of solid materials. Such mills use the principal of high speed collision and refraction of solid particles charged to the mill along with a pressurized fluid medium. Generally, a high-pressure fluid, such as steam, air or other fluid, is injected through nozzles into an oval shaped device, with the fluid expanding after passage through nozzles. The solid particles are entrained in the fluid stream and swept about the interior of the device such that they collide with each other and are pulverized. The pulverized particles are then classified with finer particles discharged from the device for use, along with spent fluid, while coarser material is recycled for further pulverizing.
It has been proposed to use such fluid energy mills for grinding of coal to a fine particle size, whereby the pulverized coal may then be mixed with oil to form a coal-oil mixture for use as a fuel. Such coal-oil mixtures are especially useful in power plants which are designed for oil combustion but which, faced with the diminishing supply and increased cost of oil, must seak other fuel sources. Coal is charged, in such systems, to a fluid energy mill along with high pressure steam, with the discharge from the mill fed to cyclones or other solids removal means, wherein the pulverized coal is collected and then admixed with oil to make the desired coal-oil mixture. The steam is then discharged to the atmosphere.
The present invention is directed towards a system for utilizing such fluid energy mills in the pulverizing of coal to form fine particles of coal to be admixed with oil in forming a fuel and means for effecting such pulverizing under conditions of safety and energy conservation.